This invention is directed to a decoder and comparator for Manchester biphasic code which does not require the use of a high frequency clock for the decoder comparator.
Manchester code is utilized for data transmission. It utilizes a mid bit phase transition to be indicative of a binary 1 bit or a binary 0 bit. U.S. Pat. No. 4,361,895 discussed certain advantages and disadvantages of Manchester code and discloses a decoder for Manchester code. This decoder, however, relies upon the use of a local clock during the decoding of the data.
U.S. Pat. No. 4,545,055 further discusses the use of Manchester or biphase code. It discusses certain military standards utilized in this code, most notably MIL-STD-1553. As with the decoder of the patent noted in the prior paragraph, the decoder of this patent also requires the use of a local clock for decoding.
In order to avoid the necessity of having to use a clock for decoding purposes, U.S. Pat. Nos. 3,979,746, 3,659,286, 3,967,061, and 4,507,794 disclose devices for recovering a clock pulse from the Manchester data itself. While the devices presented in these patents certainly all have utilitarian value, none of them provide for simultaneously also recognizing certain frame sequences within the code, such as a frame sync as per the above 1553 protocol noted in U.S. Pat. No. 4,545,055. Further, the slow speed of IC's and other devices which certain of these patents utilize inherently inhibits the self-clocking features of the patents. Thus, for instance the use of MOS elements or RC networks and the like can inherently limit the usefulness of the devices at particular frequencies.